The diagnosis by low intensity X-ray imaging and computer assisted tomography scanning (CAT scanning) of early tumors in rodents serving for safety evaluation of chemicals in carcinogenesis bioassays could greatly reduce the time required (and hence the cost) of such bioassays, especially when the test substance is carcinogenic. Combined with computerized image analysis to measure the cross sections of internal tumors, CAT scanning could for the first time permit the noninvasive continuous measurement of tumor regression under chemotherapy in small rodents. Bio-Research Consultants, Inc., in cooperation with American Science and Engineering of Cambridge, Massachusetts, which will develop a prototype MINI-CAT Scanner applicable to the study of small rodents (mice, rats and hamsters), propose to validate the method for the above purposes by the procedures outlined in the present proposal. The data obtained in this research will be published in scientific journals to enable scientists who will acquire MINI-CAT scanners to know the sensitivity, accuracy and limitations of low intensity X-ray and MINI-CAT scanning techniques applied to small rodents. This work will establish the usefulness of the low intensity MINI-CAT scanning method and will make possible the marketing of MINI-CAT equipment by AS&E to chemical and pharmaceutical manufacturers and to contract laboratories. This project will enable the applicant to offer its clients low intensity X-ray CAT scan imaging as a service utilizing equipment provided by AS&E.